Boris Johnson's environment team presses the Government to help improve
London's air quality by taxing old and new diesel cars across the UK

The Government should tax owners of diesel cars more to push drivers towards cleaner petrol and electric cars, the senior environment advisor to London mayor Boris Johnson has urged.

The current push to reward fuel-efficient cars via carbon dioxide-based VED tax has seen a huge swing to more frugal but much dirtier diesels, Matthew Pencharz told The Telegraph. “In the last 15 years we’ve seen dieselisation of the car fleet, switching from under 10 percent of the market to more than half,” he said. “But diesel has exacerbated greatly the air quality problem in London.”

Earlier this yeara study from Public Health Englandshowed that the risk of death from air pollution in central London was almost four times higher than the cleanest areas of the UK. Meanwhile in February the European Commission launched legal proceedings against the UK for exceeding agreed air pollution limits not just in London but also places like Hull, Southampton and Teeside.

Diesels emit the bulk of emissions that endanger health, with cars the main offender, according to figures released by the London Mayor’s office. The figures show cars including private-hire taxis contributed to 39 percent of smog-forming nitrogen dioxide (NO2), 28 percent of related oxides of nitrogen (NOX) and 54 percent of PM10 particulate matter.

The London Mayor’s office wants the Government to help reduced this by penalising diesels both old and new via the VED tax system. “We want a tax weighting on diesels. Over time it would retrospective,” Pencharz said. “We want to see bit less diesel and a bit more petrol.”

He justified penalising drivers of diesel cars outside London by saying the changes would benefit the whole country, not just London, Pencharz said. “The air quality challenge is a national problem.”

Pencharz will get to outline his plans when he represents the Mayor at the Parlimentary inquiry on air quality due to take place in June or July. The Environmental Audit Committee holding the inquiry has said it is "disappointed" that the Mayor himself isn't attending.

Cars are governed by Europe-wide emissions regulations that have got tougher over the years, but they failed to take into account stop-start city driving, according to Pencharz: “Euro standards 4 and 5 did not deliver the NOX reductions we were promised – they did not test for an urban style of driving,” he said.

From September a new EU6 emissions standard is being rolled out for new diesels cars that calls for the further reduction of NOX, however the Mayor is still pushing for more people switching to petrol, petrol-electric hybrid or electric powered cars, according to Pencharz.

Last year Johnson announced plans for an ultra low emission zone in London for 2020 that he stated would “deliver dramatic benefits in air quality” by switching drivers to more zero and low-emission vehicles. New black cabs will have to have to “zero-emission capable” by 2018.

Pencharz wouldn’t deny reports that the Mayor wants to ban older petrol and diesel cars from the zone, which would be confined to the current central congestion charge zone “in the first instance”.

“The Mayor’s view is that would not be reasonable to ban someone who has bought a car relatively recently. We want give people as long as they can to know that it’s coming,” he said. Consultation for the zone will begin later this year and the final plans will be announced in 2015.